Redundant bounds check when indexing array with enum in Rust 1.90 #147831
Description
Code
I tried this code:
fn test(instructions: &[Instruction], registers: [u32; 4]) -> u32 { if let Some(&instruction) = instructions.get(0) { match instruction { Instruction::A(a) => registers[a as usize], Instruction::B(b) => registers[b as usize], } } else { 0 } } #[derive(Copy, Clone)] enum Instruction { A(Register), B(Register), } #[derive(Copy, Clone)] enum Register { A, B, C, D, }I expected to see this happen: No bounds check is emitted
Instead, this happened: There's a bounds check accessing registers
Version it worked on
It most recently worked on: Rust 1.89
Version with regression
rustc --version --verbose:
rustc 1.90.0 (1159e78c4 2025-09-14) binary: rustc commit-hash: 1159e78c4747b02ef996e55082b704c09b970588 commit-date: 2025-09-14 host: x86_64-unknown-linux-gnu release: 1.90.0 LLVM version: 20.1.8 Also checked in nightly:
rustc 1.92.0-nightly (53a741fc4 2025-10-16) binary: rustc commit-hash: 53a741fc4b8cf2d8e7b1b2336ed8edf889db84f4 commit-date: 2025-10-16 host: x86_64-unknown-linux-gnu release: 1.92.0-nightly LLVM version: 21.1.3